The present invention relates to a diaphragm structure. Particularly, the present invention relates to a ceramic diaphragm structure having a thin diaphragm in a hollow portion and a joint portion of the diaphragm in a hollow portion having a special configuration.
There has conventionally been used a diaphragm structure as a member or the like constituting various kinds of sensors. The diaphragm structure has a substrate having at least one window portion and a thin film material having flexibility so as to cover the window portion. In recent years, the diaphragm structure has had particular usefulness as a piezoelectric/electrostrictive actuator.
For example, as a member constituting a sensor, a diaphragm portion of the diaphragm structure detects a flexing displacement and vibrations received from a subject to be measured by a proper detecting means. When the diaphragm structure is used as a member constituting a piezoelectric/electrostrictive actuator, a diaphragm portion of the diaphragm structure is deformed, displaced and vibrates by the piezoelectric/electrostrictive actuator, thereby generating sound or pressure in a pressurizing chamber formed inside the diaphragm structure.
Such a diaphragm structure is produced by unitarily combining a substrate as a supporter and a film member providing a diaphragm. In view of reliability, thermal resistance, anti-corrosive ability and the like, it was considered to constitute such a diaphragm structure by unitarily firing a ceramic body. The present inventors have proposed in Japanese Patent Application 62-129360 (Japanese Patent Lid-Open 63-292032) a pressure detecting apparatus or a piezoelectric/electrostrictive actuator, each of which uses a ceramic diaphragm structure obtained by being unitarily fired.
As shown in FIG. 9, such a ceramic diaphragm structure is generally obtained by firing unitary laminate composed of a first green substrate 10 having window portions 10a and a second green substrate 9 having a thin planar shape. Alternatively, as necessary, such a ceramic diaphragm is obtained by firing unitary laminate composed of the green substrates 9, 10 and another substrate such as a third green substrate 11 having throughholes 11a in communication with the window portions 10a.
If the third green substrate 11 does not have any throughhole 11a, thereby closing off the cavities, problems are caused by rising air pressure in each cavity when thermally treated, or the like, in a manufacturing process. Each of the throughholes 11a has a role of avoiding such problems. For example, when the diaphragm structure is used for a speaker, the throughhole 11a has a function of adjusting a volume of air flow and a back pressure.
There are various kinds of requirements for an element of a sensor, a speaker, an actuator, a filter, a condenser array, and the like. The requirements are increasing a surface area of a moving portion occupying a part of a surface of an element (decreasing a surface area of a stationary portion), high efficiency and miniaturization of an element by means of highly dense disposition of a plurality of moving portions, conformability to a complicated modification of a design, disposition of a plurality of driving portions each having different properties in one clement. Particularly in the case of a sensor, an element having a large surface area of a stationary portion increases a sensing loss, thereby lowering a sensing ability.
Therefore, as shown in FIG. 10, a partition wall between window portions 13a, 17a of the first ceramic substrate 13, 17 was changed from a thick one 13c to a thin one 17c (D2.ltoreq.D1) without changing a distance between the partition walls (L1=L2), thereby restraining a surface area excluding diaphragm portions (D1-D4) of a diaphragm structure by decreasing a distance between diaphragm portions with maintaining dimensions of diaphragm portions.
However, there are some problems in the diaphragm structure in which a surface area excluding diaphragm portions is restrained by decreasing a distance between moving portions by reducing a thickness of the partition wall.
First, since the partition wall 17c formed between window portions is thin, a rigidity of the first ceramic green sheet decreases. Therefore, there sometimes happens a distortion of an inner wall of a window portion, i.e., a partition wall 17c, or a burr upon punching a window portion 17a, thereby giving an unstable configuration of a diaphragm structure to be obtained.
Second, since a die for machine punching must typically have a fine configuration, the die is prone to abrasion and a short life span, and the cost for maintaining the die increases, which makes a diaphragm structure expensive, in addition to an unstable configuration of the diaphragm structure.
Third, a partition wall 17c is crushed and deformed by a pressure of lamination upon handling after punching, particularly when ceramic green sheets are laminated by being pressurized. Therefore, a diaphragm cannot have a stable configuration.
Other problems are that a diaphragm structure cannot be produced with high precision, or that various types with only a small order number cannot be produced, in view of the demand for conformity to a modification of a design of a diaphragm structure or for disposition of a plurality of diaphragm portions having various configurations.
Accordingly, the present invention is directed to providing a diaphragm structure which maintains a rigidity inherent in ceramic green sheets have in a producing process and a configuration of a diaphragm of a completed diaphragm structure and which has a smaller rate of surface area occupied by a portion excluding diaphragm portions. Further, the diaphragm structure is produced rapidly at a low cost even if a design is changed complexly or a design requires disposition of a plurality of diaphragm portions each having an individual configuration in one substrate.